ESE's works engine tuner

[philou]

Do you have more information on dellorto VHTC carburettors?

Does it use specific jet, needle and needle jet or common to other model?

Is the jet in a plenum chamber?

[lohring]

Even after a lot of work, the Wankel was a failure, in part because of seal issues. I loved the idea, though, and own a model Wankel that I flew on an RC airplane. I also respect the attempt to show the steps to improve the old idea. However, didn't Honda unsuccessfully experiment with oval pistons? See https://global.honda/heritage/episod...tonengine.html

Lohring Miller

[Frits Overmars]

Even after a lot of work, the Wankel was a failure, in part because of seal issues. I loved the idea, though, and own a model Wankel that I flew on an RC airplane. I also respect the attempt to show the steps to improve the old idea. However, didn't Honda unsuccessfully experiment with oval pistons? See https://global.honda/heritage/episod...tonengine.html

That is a nice read Lohring; here's a quote I particularly like:

World GP racing regulations limit the number of cylinders to four. Accordingly, for a four-stroke engine to be as powerful as a two-stroke unit, it has to achieve twice its normal rpm. To achieve that, the team had to enhance the intake efficiency and design a valve system with higher resistance to friction and heat buildup at high revolutions. Given these conditions, the idea was born to double the number of valves to eight. As they examined the potential valve positions in the context of their four-stroke engine layout, the team came up with an idea of changing the piston's shape from a circle to an oval.

Now allow me to tell that part of the story the way I remember it.
Honda realised that they would have to build an eight-cylinder four-stroke if they would have any chance at all to beat the four-cylinder two-strokes. But eight-cylinder engines were forbidden... "What if we remove the cylinder walls between adjacent pistons? Then we'd have a V-four instead of a V-eight!
It may not be in the spirit of the rules but it does follow the letter of the rules".

Designing, building and trying to race the NR500 (I wonder who was the first to call it the NeverReady?) turned out to be an expensive way of discovering that two-strokes are not that easily beaten. It took Honda R&D a couple of years and more than a couple of Yen to see the light and start building excellent two-stroke racers.
In-between they went rotary as well:

[katinas]

Interesting that for Daytona race Honda prepared big bore versions, NR 600 cc for the race and later with two stroke NS 550 cc. But F. Spencer use NS 550 only for practice and used 500 cc for the race.
Other very interesting Honda engine was 250 cc tandem for CR (RC) 250 prototype, or idea of oval piston for two stroke.

[pete376403]

Interesting that for Daytona race Honda prepared big bore versions, NR 600 cc for the race and later with two stroke NS 550 cc. But F. Spencer use NS 550 only for practice and used 500 cc for the race.
Other very interesting Honda engine was 250 cc tandem for CR (RC) 250 prototype, or idea of oval piston for two stroke.

Honda may have tried too many things at once - 16" wheels, monocoque frame making it hard to work on, probably other things as well.

[husaberg]

Interesting that for Daytona race Honda prepared big bore versions, NR 600 cc for the race and later with two stroke NS 550 cc. But F. Spencer use NS 550 only for practice and used 500 cc for the race.
Other very interesting Honda engine was 250 cc tandem for CR (RC) 250 prototype, or idea of oval piston for two-stroke.

They also built a turbo 250 oval piston for Freddy to try out couldn't convince the rule-makers to change the rules to allow turbos. Although Freddie tried it in practice.

the line drawing most say was for the round piston twin but note the gear driven cams
They then built a conventional round piston 250 kind of based on the VT250 with twin turbos that made over 100hp. Some say 150





Honda's web site

The NR250 Turbo was half an NR500 with twin turbochargers one for each cylinder and PCM-FI injection.
It was to replace the NR500 for Grand Prix racing. In 1983, it made 153 PS (150 HP) at 18500 RPM and 2.0 Bar pressure. Due to turbo lag (and rules changes) it never made it to the track.



The VT250RT made 150 PS (148 HP) at 11500 RPM and weighed approx. 375 lbs.
Honda found the VT250RT turbo came on boost at 7500 RPM and accelerated at twice the rate of the NS500.
Honda decided the power band was way too peaky for the rider to handle, de-tuned the engine to 90 PS (89 HP) at 11500 and wanted to put it into the 1985 Japanese model catalog as the VT250FTC, but was denied permission by the government.

Honda through a heap of graduate students at the Nr project to try new things composites USD forks side radiator small wheels, slipper clutches, carbon brakes, separate spring forks carbon frames etc.
Most were used later on the V fours.

[lohring]

Super or turbo charging is the only hope a four stroke has to develop the same power as a simple tuned pipe two stroke of the same displacement. You either need double the BMEP or double the RPM. Increased intake pressure lets you do both to some degree. You then get a much more complicated and expensive engine. Racing bodies changed the rules to nearly double the allowed displacement for four strokes. You still get a heavier, more complex engine. Even Honda learned this.

Lohring Miller

[TZ350]

2Stroke Stuffing is making progress with basic testing of the 24/7 idea. He has a normally aspirated 50cc two stroke with two carbs. A small carb/reed valve setup to get the engine up to speed. And then when its on the pipe he opens a second much larger carb that is completely open to the crank case. No reed or rotary valve. Totally open 24/7 and relying on resonance in the inlet tract.

The experiment showed promise and with some refinement should run well. It will be interesting to see if there is a power advantage.

The first time I came across this idea was when I read about a dyno test of a rotary valve two stroke single. Where at full power the rotary valve sized in the open position. The engine kept making full power until the throttle was closed and the revs drop'd. Later I saw Frits talking about the 24/7 concept. Where a pair of reeds were used to get the engine up to speed then when it was on the pipe the reeds were held open 24/7.

Attachment 336062

I think it's possible that a conventional reed starts behaving like a 24/7 inlet when the engine frequency rises above the reed's natural frequency,
but it will still offer a lot of flow resistance. Better swing the reeds out of the way altogether.

[Frits Overmars]

The video tells it all: blowback from the 24/7 carburetor whenever its throttle is opened, wich is only to be expected considering the Helmholtz resonance frequency there: conventional crankcase volume, big carb diameter, short inlet tract, low revs and infinite inlet timing.
Revving the engine higher before opening the 24/7 carb, like Alex is proposing, will help, but the best (and simplest) solution is to increase the inlet tract length.

[husaberg]

The video tells it all: blowback from the 24/7 carburetor whenever its throttle is opened, wich is only to be expected considering the Helmholtz resonance frequency there: conventional crankcase volume, big carb diameter, short inlet tract, low revs and infinite inlet timing.
Revving the engine higher before opening the 24/7 carb, like Alex is proposing, will help, but the best (and simplest) solution is to increase the inlet tract length.

Hi Frits, wouldn't it be more effective to make the bellmouth longer or better still variable?




or the Mazda 787B




seen this today make your own bellmouths the easiest way
https://imgur.com/QqXkzwu

[Frits Overmars]

Hi Frits, wouldn't it be more effective to make the bellmouth longer or better still variable?

It might be, in combination with fuel injection. But when using a carburetor, as Alex is doing in his latest 2Stroke Stuffing video ( https://www.youtube.com/watch?v=RxjD_wLvwrE ) a bellmouth is definitely a bad idea because it would put the carb somewhere in the middle of the inlet tract, instead of at the very beginning, where it ought to be.
'Somewhere in the middle' there is a real risk of pulsating flow going to and fro over the needle jet, picking up fuel each time, forming an ultra-rich mixture that may drown the engine.

seen this today make your own bellmouths the easiest way
https://imgur.com/QqXkzwu

The easiest way to make a bellmouth maybe, but not a good way. An efficient bellmouth has a properly radiused entry, guiding air from all directions into the inlet tract.

[husaberg]

It might be, in combination with fuel injection. But when using a carburetor, as Alex is doing in his latest 2Stroke Stuffing video ( https://www.youtube.com/watch?v=RxjD_wLvwrE ) a bellmouth is definitely a bad idea because it would put the carb somewhere in the middle of the inlet tract, instead of at the very beginning, where it ought to be.
'Somewhere in the middle' there is a real risk of pulsating flow going to and fro over the needle jet, picking up fuel each time, forming an ultra-rich mixture that may drown the engine.

The easiest way to make a bellmouth maybe, but not a good way. An efficient bellmouth has a properly radiused entry, guiding air from all directions into the inlet tract.

Three times past the main jet.........

[speedpro]

3D printed for my 125

[speedpro]

Alex is planning a simple injection system on the 24/7 port. The carb was just a test as he just had to give it a try.

[F5 Dave]

Have we seen in the cases? Looks like trying to go through the crank webs?.?